As is well known, a mixture of potassium chloride and kieserite (magnesium sulfate), separated electrostatically from ground crude salt, may be used for the production of potassium sulfate. For example, such a mixture of potassium, chloride and kieserite may be reacted in an integrated two step process, wherein the first step comprises reacting the salt mixture with a sulfate liquor that is obtained from the second step of the process to form a mixture of a potassium magnesium double sulfate salt such as, for example, schoenite, K.sub.2 SO.sub.4.MgSO.sub.4.6H.sub.2 O or leonite, K.sub.2 SO.sub.4.MgSO.sub.4.4H.sub.2 O and potassium chloride. This mixture may then be subjected to the second step wherein the mixture is converted with water into potassium sulfate and the sulfate liquor that is used in the first processing step. The resulting potassium sulfate is separated as the product, while the sulfate liquor is returned to the process. Such a process is proposed, for example, in the German AS No. 1,923,514.
Although processes of the above type may be utilized to produce potassium sulfate, they are characterized by an inherent disadvantage since kieserite reacts relatively slowly. Accordingly, efforts have been made to change the relatively slow reacting kieserite into a faster reacting form so as to facilitate its conversion to potassium sulfate. For example, in accordance with one previously known process, the potassium chloride-kieserite mixture may be activated by grinding the same to a very finely divided state. In still another known process, the mixture may be activated by heating the same to temperatures above 200.degree. C. These activating measures however, require an additional expenditure of apparatus and power.